This invention relates generally to industrial liquid pressure filter apparatus and methods, for liquid-to-be-filtered having (1) a carrier liquid, (2) coalescing solids particles which tend to stick together to bridge and thus blind a filter element gap sized larger than the width of such particles, and (3) larger impurity elements to be filtered out and sized larger than such a filter element gap.
Ultrasonic energy has been applied to prior flow separation situations-but, insofar as known to Applicants, not to the field to which the present invention is directed.
More particular, prior applications of ultrasonic energy in flow separation have included the following.
Thompson U.S. Pat. No. 4,253,962 intends to avoid use of chemical cleaning agents for cleaning ion selective membranes, such as reverse osmosis and electrodialysis membranes, of impurities to be filtered out, by applying ultrasonic energy below the threshold of cavitation in a manner to avoid destruction of the membrane by standing waves. Such a membrane is not self-supporting but rather requires a perforate rigid backing (for example, a mesh structure in turn backed by a rigid perforated tube.
Sieg U.S. Pat. No. 5,298,161, Goyal U.S. Pat. No. 5,059,331 and a pending U.S. Application (Attorney Ref: R-P Case 27), now U.S. Pat. No. 6,251,294, assigned to the Assignee of the present invention disclose filtration systems with alternate filtration and cleaning cycles. Ultrasonic energy is applied to supplement or substitute for backwashing, during the cleaning cycle (not during the filtration cycles) to remove impurities to be filtered out, from the input side of the filter, and thereby renew the filter for another cycle of filtration.
However, none of these pressure liquid applications of ultrasonic energy deals with the above stated field of the present invention.
Ultrasonic energy has also been used to agitate an open screen used to separate, for example, dry contaminants from dry corn kernels. However, such application is even more remote from the above stated field of the present invention.
Turning more particularly to prior art in the field of the present invention, a series of inventions are disclosed and claimed in U.S. patents assigned to the Assignee of the present invention, and issued over approximately the last four decades. The latter patents apply to the field of the present invention and have attempted to overcome the problem to which the present invention is directed, as follows.
Petter, et al. U.S. Pat. No. 3,161,159 recognized, as to liquid solutions, suspensions and the like having a high solids content, particularly certain liquids of a viscous nature or otherwise having a high solids content such as colloidal gels, lime and clay slurries, starch solutions, clay coatings and the like in which the solids tend to coagulate or coalesce, that the filtering out of large impurity elements is a difficult problem.
For convenience herein, such a difficult-to-filter liquid is herein referred to as a composite liquid, which may be described as comprising (1) a carrier liquid and (2) coalescing solids particles which tend to stick together. Such coalescing solids particles, even at relatively low flow rates, tend to bridge, rather than pass with the carrier liquid through, the filtering gaps in the filter element.
Petter""s disclosed solution to the problem involved suspending elongate pressure air supply and exhaust hoses in the filter housing flanking the filter element, and from the hoses suspending a casing in the bottom of the housing below the filter element. The casing contains a circular path generally coaxial with the filter element and housing. A weighted ball is pushed by air pressure from the suspending air hoses along the circular path. The orbiting of the ball therein moves the casing and lower air hose portions in respective circular orbits in the liquid space inside the filter housing and outside the filter element, and thus moves the liquid-to-be-filtered in the housing in an attempt to maintain the coalescing solids particles in suspension in the carrier liquid. Reece U.S. Pat. No. 3,692,178 discloses a generally similar arrangement.
To attempt to improve on the aforementioned Petter and Reece inventions, Reece U.S. Pat. No. 3,870,640 fixed an air powered ball casing to the bottom of the suspended filter element and led the air supply and exhaust hoses through the open top (outlet) of the filter element and down inside the filter element to the air-powered ball casing at the bottom of the filter element, to vibrate the filter element. This approach was advanced by DeVisser, et al. U.S. Pat. No. 4,642,188 by fixing a single air-powered ball casing to the bottom of a group of three, side-by-side filter elements, to vibrate more filtering area in a single filter housing.
Thereafter, to attempt to improve on the aforementioned DeVisser invention, particularly to make more uniform the filter element vibration along the length of the filter element, Rishel, et al. U.S. Pat. No. 4,836,922 used an air powered ball casing to pendently support the top of the filter element group from the overlying top of the filter housing.
Thereafter, Davis et al. U.S. Pat. No. 5,084,176 reoriented the air powered ball casing of Rishel to change the plane of travel of the circulating ball to vibrate the filter element axially rather than radially, for use with a liquid-to-be-filtered less sensitive to coalescing particle sheer than in the Rishel patent.
Thus, over about the last four decades, the sequence of invention in the field of the invention has used an air powered ball casing vibrator, first to directly agitate liquid in a filter housing, then to directly vibrate the bottom of a filter element, then to directly vibrate the bottom of a group of the filter elements, then to attach the top of a filter element group to the filter housing and vibrate the filter element group (initially laterally and later axially).
While many of these air powered vibrator equipped filter units are still in satisfactory service, the Assignee of the present invention has now discontinued their manufacture (except as replacements for customer in-the-field older units), and has switched the sequence of invention, in the field of the present invention, to mechanically cleaned filter elements, examples of which it now manufactures and markets in its DCF(trademark) line of filter units.
More particularly, Davis U.S. Pat. No. 5,198,111; Davis et al. U.S. Pat. No. 5,527,462 and Vander Ark U.S. Pat. No. 5,569,383, all assigned to the Assignee of the present invention, each require, per housing, a single relatively large diameter cylindrical filter element in which filtration flow direction is reversed (from the air powered vibrator equipped filter units above discussed) namely, from inside out, wherein a mechanically driven cleaning member moves slowly but continuously along the inlet surface of the filter element and mechanically wipes or scrapes coalescing solids particle bridges from the filter element gaps back into suspension in the liquid-to-be-filtered.
Accordingly, the recent prior art developments by the present Assignee have eliminated vibrating devices in favor of the above mentioned wiper/scraper equipped filter units, to try to overcome the continuing problem in the field of the present invention.
Such scraper/wiper equipped filter units have been commercially successful in a variety of filtering uses, in some instances in which a composite liquid includes particularly aggressively coalescing solids particles and the filter element blinds at less than a commercially acceptable filtration flow rate.
Accordingly, the objects and purposes of the invention include provision of methods and apparatus for preventing bridging, and thus continuing filtration flow, through a liquid pressure filter unit, of liquid-to-be-filtered of the kind having (1) a carrier liquid (2) coalescing solids particles which tend to stick together to bridge and thus blind a filter element gap sized larger than the width of the said particles, and (3) larger impurity elements to be filtered out of said liquid-to-be-filtered and sized larger than such a filter element gap, and doing so at substantially enhanced flow rates approaching or exceeding commercial acceptance levels.
Other objects and purposes of the invention will be apparent to persons acquainted with apparatus and methods of this kind upon reading the accompanying specification and inspecting the accompanying drawings.
The invention includes methods and apparatus for increasing the continuous filtering flow rate through a pressure liquid filter unit of liquid-to-be-filtered having (1) a carrier liquid, (2) coalescing solids particles which tend to adhere and bridge filter element gaps sized substantially larger than said particles and (3) larger impurity elements to be filtered out of said liquid-to-be-filtered and sized larger than such filter element gap, comprising:
providing a pressure liquid filter unit having a housing with an inlet and an outlet and containing a filter element having gaps, a given gap being sized to reliably pass the carrier liquid and coalescing solids particles at a first relatively low liquid flow rate, but blocking coalescing solids particles passage therethrough due to bridging of said gaps by the coalescing solids particles at a relatively high liquid flow rate;
simultaneously flowing the liquid-to-be-filtered under pressure through the inlet into the housing at the relatively high flow rate and applying ultrasonic energy to the liquid-to-be-filtered in the housing;
at an ultrasonic frequency agitating the coalescing solids particles adjacent said gap and thereby passing the carrier liquid and coalescing solids particles through the gap at the relatively high flow rate without bridging and blinding of the gap by the coalescing solids particles.